Various materials and processes have been described for use in the production of microporous films. Microporous films are well known for use in various applications, typically where air and moisture permeabilities are desired together with liquid barrier properties.
In particular, microporous films and composites hold promise as inexpensive barrier materials for surgical drapes, protective clothing worn during medical or dental procedures, or other instances where an individual may be exposed to blood or body fluids that may contain pathogenic organisms. Microporous films and composites can prevent the penetration of blood and blood-borne pathogens if the microporous film can be manufactured with a reliably small and controlled maximum pore size. The test methods ASTM F 1670-03 and ASTM F 1671-03 have been developed to test the resistance of barrier materials to penetration by synthetic blood and viruses, respectively. Unfortunately, many microporous films made by standard methodologies fail one or both ASTM penetration tests because the maximum pore size is too large, the pore size is not controlled adequately, or the microporous films are prone to pinholes, tearing and other defects during fabrication or use.
Many of the conventional processes for controlling pore size in microporous films involve the use of expensive additives and/or employ cumbersome processing techniques which are not suitable for large scale production. Accordingly, there is a continuing need for improving the barrier properties of microporous polymer films and composite materials employing such films, by creating adequately small pores in the films and by controlling the maximum pore size and pore-size distribution of the microporous films, particularly while maintaining high production efficiency of such films using standard extrusion equipment and readily available raw materials.